Stack overflow from package:analyzer LeastUpperBoundHelper.getLeastUpperBound

[modulovalue]

Consider the code example from #53254 and paste it into DartPad:

void foo<T extends List<S>, S extends List<T>>(T x, S y) {
  var a = (x == y) ? x : y;
}

Notice the confusing error message:

I expected the error message to be descriptive and not confusing.

[devoncarew]

It looks like we're getting an error from the analysis server's analysis.getError call (not a crash, but an error result):

RequestError(method: analysis.getErrors, code: GET_ERRORS_INVALID_FILE, message: Error during `analysis.getErrors`: invalid file)

[devoncarew]

@scheglov - I see very strange behavior when editing this snippet in a local editor. Initially I see no analysis issues. If I remove some parts of the local variable assignment I see some. Further edits can cause the issues to update or not in unpredictable ways. It doesn't look like the analysis server is crashing but there's definitely some analysis oddities.

Switching the ternary from x : y to x : x yields predictable analysis:

void foo<T extends List<S>, S extends List<T>>(T x, S y) {
  var a = (x == y) ? x : x;
}

The value of the local variable 'a' isn't used.

[scheglov]

There is an exception inside the analyzer.

  Stack Overflow
  #0      _AssertionError._evaluateAssertion (dart:core-patch/errors_patch.dart:56:3)
  dart-lang/dart-pad#1      _HashBase._indexSizeToHashMask (dart:collection-patch/compact_hash.dart)
  dart-lang/dart-pad#2      _LinkedHashSetMixin._init (dart:collection-patch/compact_hash.dart:828:28)
  dart-lang/dart-pad#3      _LinkedHashSetMixin._rehash (dart:collection-patch/compact_hash.dart:811:7)
  dart-lang/dart-pad#4      _LinkedHashSetMixin._add (dart:collection-patch/compact_hash.dart:873:7)
  dart-lang/dart-pad#5      _LinkedHashSetMixin.add (dart:collection-patch/compact_hash.dart:847:12)
  dart-lang/dart-pad#6      SetBase.addAll (dart:collection/set.dart:58:33)
  dart-lang/dart-pad#7      _CompactLinkedIdentityHashSet.addAll (dart:collection-patch/compact_hash.dart:1092:11)
  dart-lang/dart-pad#8      TypeSystemImpl.greatestClosure (package:analyzer/src/dart/element/type_system.dart:623:22)
  dart-lang/dart-pad#9      LeastUpperBoundHelper.getLeastUpperBound (package:analyzer/src/dart/element/least_upper_bound.dart:565:33)
  dart-lang/dart-pad#10     TypeSystemImpl.leastUpperBound (package:analyzer/src/dart/element/type_system.dart:1572:35)
  dart-lang/dart-pad#11     InterfaceLeastUpperBoundHelper.compute (package:analyzer/src/dart/element/least_upper_bound.dart:76:31)
  dart-lang/dart-pad#12     LeastUpperBoundHelper.getLeastUpperBound (package:analyzer/src/dart/element/least_upper_bound.dart:647:19)
  dart-lang/dart-pad#13     LeastUpperBoundHelper.getLeastUpperBound (package:analyzer/src/dart/element/least_upper_bound.dart:584:14)
  dart-lang/dart-pad#14     LeastUpperBoundHelper.getLeastUpperBound (package:analyzer/src/dart/element/least_upper_bound.dart:566:14)
  dart-lang/dart-pad#15     TypeSystemImpl.leastUpperBound (package:analyzer/src/dart/element/type_system.dart:1572:35)
  dart-lang/dart-pad#16     InterfaceLeastUpperBoundHelper.compute (package:analyzer/src/dart/element/least_upper_bound.dart:76:31)
  dart-lang/dart-pad#17     LeastUpperBoundHelper.getLeastUpperBound (package:analyzer/src/dart/element/least_upper_bound.dart:647:19)
  dart-lang/dart-pad#18     LeastUpperBoundHelper.getLeastUpperBound (package:analyzer/src/dart/element/least_upper_bound.dart:584:14)
  dart-lang/dart-pad#19     LeastUpperBoundHelper.getLeastUpperBound (package:analyzer/src/dart/element/least_upper_bound.dart:566:14)
  dart-lang/dart-pad#20     TypeSystemImpl.leastUpperBound (package:analyzer/src/dart/element/type_system.dart:1572:35)
  dart-lang/dart-pad#21     InterfaceLeastUpperBoundHelper.compute (package:analyzer/src/dart/element/least_upper_bound.dart:76:31)
  dart-lang/dart-pad#22     LeastUpperBoundHelper.getLeastUpperBound (package:analyzer/src/dart/element/least_upper_bound.dart:647:19)
  dart-lang/dart-pad#23     LeastUpperBoundHelper.getLeastUpperBound (package:analyzer/src/dart/element/least_upper_bound.dart:584:14)
  dart-lang/dart-pad#24     LeastUpperBoundHelper.getLeastUpperBound (package:analyzer/src/dart/element/least_upper_bound.dart:566:14)
  dart-lang/dart-pad#25     TypeSystemImpl.leastUpperBound (package:analyzer/src/dart/element/type_system.dart:1572:35)

[devoncarew]

Thanks for the investigation! I'll bump this issue over to the sdk repo.

[modulovalue]

Note that this is a known issue, see #53254 (comment) by @eernst for details.

I have suggested one possible solution here: #53254 (comment). It is not meant to resolve the issue, but to detect it and to fail early before the stack overflow occurs. This issue appears to have been fixed on stable, but it crashes the compiler again on beta. (#53254 (comment))

[modulovalue]

I'll bump this issue over to the sdk repo.

@devoncarew This issue wasn't necessarily meant to resolve the underlying issue that causes the analysis to fail, but to point out that DartPad is outputting what appears to be raw unprocessed output from the analyzer.

That is, I expected to see an error message like the following: